When transporting hydrocarbons or similar liquid or gaseous substances from one location to another, across a body of water, use of a subsea pipeline is often preferable to the transport of hydrocarbons by using ships or aircraft, especially when a frequent or continuous need exists to transport such substances. As a result, the sea floor contains numerous pipelines, especially in regions of the world having a large number of hydrocarbon production and refining facilities. Many subsea pipelines rest on the seabed, though to protect pipelines from damage, it is preferred to bury pipelines underneath the sea floor.
Previously, when use of a subsea pipeline is no longer desired, due to damage or simply due to the cessation of a need to transport substances to locations along the pipeline, the pipeline would simply be left in place. Due to its placement underneath the sea floor, the presence of the abandoned pipeline did not present a significant concern unless unearthed by severe weather, tectonic activity, or other conditions. However, recent regulations have begun to incentivize, if not require, the removal of buried subsea pipelines when no longer in use.
While an abundance of equipment exists to facilitate the proper placement of subsea pipe segments for use, without damaging the pipeline or coating, very little specialized equipment exists for the removal of buried subsea tubulars. Because recovered segments of subsea pipelines are primarily only useful as salvage/scrap metal, the propensity of damaging, deforming, or otherwise modifying the tubulars to be recovered is not a concern, and various methods for retrieving pipe segments from the sea floor have been cobbled together using equipment not specifically intended for such a purpose.
For example, a conventional method for retrieving a segment of subsea pipeline involves manually digging an excavation area at each end of the segment (e.g., by divers, ROVs, or similar manual means), severing the pipe segment at each end, then attaching one end of the pipe segment to a cable, either directly (e.g., by cutting a hole in the sidewall of the pipe and securing the cable), or by using a connector designed to engage the interior or exterior of the severed end. The unsecured end of the cable is then allowed to float to the surface, assisted by a buoy, float, or similar attachment. A tugboat or similar vessel is then used to transport the floating end of the cable to an offshore platform or ship—normally a lift barge having a winch or a similar type of pulling device thereon, which is used to pull the cable and retrieve the tubular to the vessel. The lift barge must be positioned a significant distance away from the severed end of the tubular to facilitate pulling in a curved, “J” shaped path; pulling on a buried pipe segment, using a force with too great of a vertical component, can cause the lift barge to sway or topple due to the counter-force applied by the buried tubular. It should be noted that lift barges and similar vessels are not specifically designed or intended for such a purpose, and are subject to possible damage, falling, and similar hazards.
Once a tubular segment has been hoisted to the surface, it can be stored on the deck of the lift barge for subsequent transport (e.g., via movement of the lift barge or by unloading the tubular to an adjacent vessel) to a processing facility; however, the transport of a number of tubular segments from the deck of a lift barge to an adjacent vessel requires the time-consuming manual lifting and manipulation of each segment using a crane or similar device, which can create a potentially dangerous environment for personnel required to engage and disengage tubular members from the crane. Some vessels include processing equipment (e.g., cutters) positioned thereon, such that a retrieved tubular segment can be cut on-site to facilitate storage and transport; however, after processing a first tubular segment, manual intervention by personnel is normally necessary to engage and retrieve a subsequent tubular segment to the deck of the vessel. Additionally, the cutting and processing of tubulars on a vessel can be hindered or rendered impossible during unfavorable weather conditions.
A need exists for efficient systems and methods of unearthing, transporting, and/or processing subsea pipelines and similar tubular members that minimize the amount of manual intervention required by personnel, e.g., to engage and disengage cables from pipe segments and equipment.
A need also exists for systems and methods that enable safer unearthing, transporting, and/or processing operations for subsea pipelines than conventional alternatives.
A further need exists for systems and methods that can enable generally continuous movement and on-site processing of subsea pipelines during circumstances when transport of pipe segments may not be desirable.
Embodiments usable within the scope of the present disclosure meet these needs.